1. Field of the Invention
The present invention relates to an image forming apparatus with a fixing apparatus for fixing a developer image on a sheet of paper.
2. Description of the Related Art
An image forming apparatus utilizing a digital technique, such as an electronic copying machine, is equipped with a fixing apparatus for fixing, to a sheet of paper, an image of a melted developer by pressure.
The fixing apparatus comprises a heating member for melting a developer, such as toner, and a pressure member for applying a predetermined pressure to the heating member, a predetermined contact width (nip width) being defined between the contact region (nip portion) of the heating and pressure members. When a sheet of paper with an image of a developer melted by the heating member is passed through the nip portion, the image is fixed on the sheet by pressure from the pressure member. In recent years, heating apparatuses have been utilized in which a thin metal conductive layer is formed outside a heating member and is heated using induction heating.
To secure a sufficient nip width between the heating member and the pressure member, the heating member incorporates a roller-shaped elastic member located inside the metal conductive layer. Since the thermal expansion rate of the metal conductive layer is greater than that of the elastic member, the elastic layer will raise from inside the metal conductive layer when they are thermally expanded. As a result, the heating member is hardened, therefore it is difficult to secure a sufficient nip width.